1. Field of the Invention
This invention lies in the field of polyhydroxylated polymers of bisphenols and epichlorohydrin, and, more particularly, of irradiation cross-linkable thermostable polymer systems having a plurality of hydroxyl groups per polymer repeating unit which groups are adapted for reaction with light responsive groups or compounds.
2. Prior Art
It is known to manufacture multilayer wirings by pressing together superimposed thin films to form laminates containing a desired corresponding conduction image by means of adhesive films interlayered between such thin films. The resulting thin film laminates form layers of insulating material between individual interconnect levels. After multilayered printed circuit boards have been produced, the line connections and contact locations between the individual layers are produced by borings and subsequent platings of these bores.
In order to avoid crack formation in the contact layer or in the intermediate layers, as well as to avoid delamination effects, when soldering, or when experiencing alternating temperature stresses, the procedure described above has been improved so that the thin film laminates are copper-laminated on both sides, and the copper films are coated with a photo sensitive (e.g. a photo resist) lacquer layer. This layer, which can be comprised either of a negative or a positive lacquer, is covered with a selected corresponding mask, then imaged (exposed), and developed. The remaining, developed portions of such a resin layer serve as sites which protect the underlying copper in a subsequent etching operation of the exposed copper. Thus, a desired conductive pattern arises after the removal of the copper by etching, while the photo imaged and developed resist lacquer layer adheres to the copper layer. The lacquer residue layers are removed thereafter either with organic solvents or mechanically, and a next layer is then applied thereover.
In order to avoid damage to the surface of the synthetic resin layer needed for the building up of the laminates, particularly the damage caused in the removal of the synthetic resin, German patent application DE-PS No. 23 42 407 proposes the employment of an organic material as a light-sensitive material which contains a compound with epoxide groups and with groups hardenable upon exposure to electromagnetic radiation. The resin should contain about two epoxide groups per molecule. The parts of the light-sensitive layer which are pre-hardened by such a radiation exposure are subjected to a thermal aftertreatment utilizing a heat-activatable hardener for epoxy resins, and, accordingly, such parts are left on the carrier film. The pressing together of the individually coated and treated carrier films is executed upon interposition of adhesive films between adjacent such carrier films. The adhesive films are comprised of a glass fabric impregnated with an epoxy resin and a hardener for the epoxy resin. It is thus of significance that the cross-linking of the resin existing after such an exposure has not progressed to such a degree that the resultant lacquer has become completely insoluble and unmeltable. Hence, the epoxide groups remaining in the lacquer layer are available to enter into a cross-linking reaction in a later pressing of a layer of such resin to a further ply of adhesive film, or, alternatively, of, prepreg (i.e. a glass fiber fabric pre-impregnated with resin, or a film comprised of a cross-linkable resin without glass fiber reinforcement). In the epoxy resin employed for the composition of this material, in such a later pressing, there must be present an adequate number of reactable groups for achieving a substantially complete cross-linking of the epoxide groups present in the resist lacquer.